Some vehicle engine systems utilizing direct in-cylinder injection of fuel include a fuel delivery system that has multiple fuel pumps for providing suitable fuel pressure to fuel injectors. This type of fuel system, Gasoline Direct Injection (GDI), is used to increase the power efficiency and range over which the fuel can be delivered to the cylinder. GDI fuel injectors may require high pressure fuel for injection to create enhanced atomization for more efficient combustion. As one example, a GDI system can utilize an electrically driven lower pressure pump (i.e., a fuel lift pump) and a mechanically driven higher pressure pump (i.e., a direct injection pump) arranged respectively in series between the fuel tank and the fuel injectors along a fuel passage. In many GDI applications the lift fuel pump initially pressurizes fuel from the fuel tank to a fuel passage coupling the lift fuel pump and direct injection fuel pump, and the high-pressure or direct injection fuel pump may be used to further increase the pressure of fuel delivered to the fuel injectors. Various control strategies exist for operating the higher and lower pressure pumps to ensure efficient fuel system and engine operation.
In one approach to control the lift fuel pump, shown by Ulrey and Pursifull in U.S. Pat. No. 7,640,916, voltage (and current) provided to the lift fuel pump can be continuous or pulsed based on a number of parameters. The parameters include a volume of fuel in an accumulator located between the lift and direct injection fuel pumps, engine speed and load, and an amount of fuel supplied to the engine. In one example control scheme, when the efficiency of the direct injection fuel pump decrease below an efficiency (or effectiveness) threshold, the lift fuel pump is energized. In this example, the lift pump energy input may cease when the lift pump pressure rises and pressurizes the accumulator located downstream from the lift pump. In another embodiment, the lift pump efficiency is used to determine when activation of the lift pump occurs. If the lift pump efficiency decreases, then fuel vapor may be forming at the pump inlet such that lift pump pressure needs to be increased to increase efficiency of the injector pump.
However, the inventors herein have identified potential issues with the approach of U.S. Pat. No. 7,640,916. First, energizing the lift pump with a pulse of voltage (and current) until a threshold pressure is reached or the lift pump pressure rises may not be the most energy efficient control scheme on which to base pump pulsing. As explained in further detail later, energizing the lift fuel pump for a predetermined time period may be more beneficial to energy-efficient pump operation. Furthermore, the lift pump control scheme depends on sensors such as a pressure sensor to determine when to cease applying voltage to the lift pump (resulting in a voltage pulse of variable duration). As such, continuous and relatively accurate feedback may be needed to ensure reliable operation of the lift fuel pump. Control schemes that do not need feedback (i.e., open loop control) may be more beneficial for more robust pump operation for certain fuel systems.
Thus in one example, the above issues may be at least partially addressed by a method, comprising: operating a lift fuel pump in a pulsed energy mode for a discrete time duration only upon detection of a threshold fuel volume expelled by a direct injection fuel pump positioned downstream of the lift fuel pump; and switching operation of the lift fuel pump to a continuous energy mode when vapor pressure is detected at an inlet of the direct injection fuel pump. In this way, by operating in the pulsed energy mode, energy may be conserved compared to operating entirely in the continuous energy mode. Furthermore, by switching between the two energy modes, robust operation of the lift fuel pump may be provided wherein the continuous mode is activated when vapor is detected, thereby allowing the pump to operate and mitigate the presence of fuel vapor.
In some embodiments, the algorithm for controlling the lift fuel pump may be alternatively implemented by detecting a threshold volume of fuel injected instead of a threshold volume fuel pumped through the direct injection fuel pump. Furthermore, to continuously operate the lift fuel pump until vapor is no longer detected, alternatively this can be implemented by applying a predetermined pulse duration upon detection of vapor and continuously repeating the pulse as long as vapor is detected. As such, this method may include operating the lift fuel pump predominantly via an open loop pulsing scheme, thereby enabling a minimum lift pump energy control scheme that may be backed up with an algorithm that applies lift pump energy if vaporization at the DI pump inlet is detected.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.